Tachykinin immunoreactivity in the parasitic flatworm Diclidophora merlangi and its fish host the whiting (Merlangius merlangus): radioimmunoassay and chromatographic characterisation using region-specific substance P and neurokinin A antisera.

1. Tachykinin immunoreactivity has been quantified and chemically characterised in extracts of the monogenean parasite, Diclidophora merlangi and its fish host, Merlangius merlangus, by means of four tachykinin radioimmunoassays interfaced with gel permeation chromatography and reverse-phase HPLC. 2. Of the two tachykinins identified in parasite tissue, one was SP-like and the other was NKA-like, although neither was identical to previously identified tachykinins. 3. Three tachykinins were identified in extracts of whiting GI tract, one of which was a neuropeptide and also occurred in whiting brain. 4. The parasite and fish tachykinins had different molecular weights and elution profiles in HPLC analyses, and were therefore chemically distinct.